Internal reaction steam turbine cooling arrangement

ABSTRACT

A rotor of a turbomachine includes a rotor drum located at a central axis and a plurality of buckets secured to the rotor drum. A first reaction stage includes axial entry dovetailed buckets. An axial passage for cooling flow is provided along a mating surface between the bucket dovetail and the dovetail slot in the rotor drum. Cool steam at taken between a first stage bucket and a second stage nozzle and passed through the axial passage to a low pressure sink at an upstream end of the rotor.

BACKGROUND OF THE INVENTION

The invention generally relates to turbomachine rotors. Morespecifically, the present disclosure relates to cooling of steam turbinerotors.

As steam turbine systems rely on higher steam temperatures to increaseefficiency, steam turbines, especially those utilizing drum rotorconstruction, must be able to withstand the higher steam temperatures soas not to compromise the useful life of the rotor. Materials that aremore temperature-resistant may be used in the rotor construction, butuse of such materials often substantially increases the cost of rotorcomponents. High pressure, lower temperature steam may be used as acoolant for the rotor, but use of this coolant from a source outside ofthe steam turbine can significantly increase cost of the rotor anddegrade the rotor performance.

It would be desirable to provide a low cost means to maintain the drumrotor of a turbomachine so as not to degrade rotor performance withoutthe need to utilize expensive temperature-resistant materials.

BRIEF DESCRIPTION OF THE INVENTION

According to a first aspect of the invention, a rotor of a turbomachineis provided. The rotor includes a rotor drum disposed at a central axis.A plurality of dovetailed buckets for a stage of the turbomachine areprovided. The plurality of dovetailed buckets are secured to the rotordrum at mating surfaces within corresponding dovetailed slots cut in therotor drum. At least one cooling passage is formed within the rotor drumfor the stage of the turbomachine. A low pressure sink disposed at anupstream end of the rotor drum is receptive of a coolant flow throughthe cooling passage.

According to another aspect of the present invention a multi-stage steamturbine is provided. The steam turbine includes a stator disposed at acentral axis and a rotor disposed radially inboard of the stator. Therotor includes a rotor drum and a plurality of dovetailed buckets for astage of the steam turbine. The plurality of dovetailed buckets aresecured to the rotor drum at mating surfaces within a correspondingdovetailed slots cut in the rotor. At least one cooling passage isformed within the rotor drum for the stage of the turbomachine. A lowpressure sink disposed at an upstream end of the rotor is receptive of acoolant flow through the cooling passage.

According to a further aspect of the present invention, a method forinstalling axial entry dovetailed buckets into dovetail slots of a stageof a drum rotor is provided. The method includes inserting twist lockdevices into an axial through-hole in a base of a dovetail slot of astage of a drum rotor for each of the dovetailed buckets. A half-head ofa front head of the twist lock device is oriented in an inward radialdirection to allow entry of the dovetailed bucket into the dovetailslot. A spacer is temporarily installed in a space in the drum rotorbetween a stage and a succeeding stage. The dovetailed bucket is fullyinserted into the dovetail slot of the stage of the rotor drum. Thehalf-head of the front head of the twist-lock device is oriented in anoutward radial direction to lock the bucket in place. The spacer isremoved.

These and other advantages and features will become more apparent fromthe following description taken in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood when the following detaileddescription is read with reference to the accompanying drawings in whichlike characters represent like parts throughout the drawings, wherein:

FIG. 1 is a partial cross-sectional view of an embodiment of a steamturbine;

FIG. 2 illustrates a radial view of a sector of a first stage with axialfemale tree dovetail slots cut in the drum rotor;

FIG. 3 illustrates a twist lock device adapted for holding axial entrydovetailed buckets in axial dovetailed slots;

FIG. 4 illustrates the twist lock device in place within the femaledovetail slot in preparation for axial insertion of bucket dovetail;

FIG. 5 illustrates an axial cutaway view of a stage sector of a turbineincluding buckets with male dovetails installed in female dovetail slotsof a drum rotor;

FIG. 6 illustrates a wheel staking groove in the wheel (rotor) face;

FIG. 7 illustrates an expanded radial view of a cooling space between amale dovetail of the bucket and a slot in a drum rotor;

FIG. 8 illustrates an axial view of an embodiment of axial entry bucketwith a cooling passage for cooling the rotor drum;

FIG. 9 illustrates an axial view of an embodiment of a reaction stagewith a cooling passage for cooling the rotor drum; and

FIG. 10 illustrates a tangential entry bucket of a first reaction stagewith a cooling passage in a root that utilizes higher downstreampressure steam from a bucket of a reaction stage to cool the drum-rotor.

DETAILED DESCRIPTION OF THE INVENTION

The detailed description explains embodiments of the invention, togetherwith advantages and features, by way of example with reference to thedrawings.

The present invention has many advantages including providing coolingfor a reaction stage of a drum rotor in order to preserve life of therotor and permit the rotor to be formed with standard rotor materialsinstead of expensive materials that are temperature resistant. The firststage of a rotor for a steam turbine is generally exposed to the highesttemperatures and pressures. Therefore it is desirable to provide coolingin particular for the first stage section of the rotor drum. Due tonegative root reaction in the first stage, the temperature out theoutlet of the stage bucket will be cooler than the inlet to the stagebucket but the pressure at the outlet of the stage bucket will be higherthan the pressure at the inlet. Hence steam at the outlet of the stagebucket at a higher pressure than the inlet to the stage bucket may beused to force the cooler steam downstream from the bucket through a pathwhich cools the first stage of the drum rotor and which discharges to alow pressure sink. Hence, an arrangement is provided to extract a lowertemperature steam downstream from a stage in a reaction turbine withdrum-rotor construction by a cooling passage that is formed by arrangingaxial entry dovetails over the axial slots cut on the drum-rotor. Thecooling passage is formed within the drum-rotor at the mating surfacesof the drum-rotor and the dovetail. This will allow the cooling flow topass through the dovetails and later mix with the flow leaking to thepacking side from the downstream side of the first nozzle. This mix flowwill flow from the packing side and cool the drum-rotor.

The above-described arrangement may provide for performance gain byallowing more flow to pass over the first stage bucket than a standarddesign. The arrangement also allows cooling directed to the hightemperature zones of a reaction/impulse rotor. Further with theadvantageous cooling, there is no need for costly material at higheroperating temperature. Additionally, no new significant major componentsneed to be added to implement the cooling.

Shown in FIG. 1 is an embodiment of a turbomachine, such as a steamturbine with an inventive cooling mechanism for the rotor. The steamturbine 10 includes a rotor 12 rotatably disposed at an axis 14 of thesteam turbine. A first stage of the turbine includes a nozzle buckets 16are secured in a plurality of bucket slots 18 in a rotor drum 13 and aretypically arranged in a number of rows, or stages, that extend around acircumference of the rotor 12 at axial locations along the rotor 12. Aplurality of stationary nozzles 20 are secured in a plurality of nozzleslots 22 in a stator 24 of the steam turbine 10. For example, the nozzleslots 22 may be located in an inner carrier of the stator 24. Thenozzles 20 are arranged in circumferential stages that are locatedbetween stages of buckets 16. The rotor 12 and the stator 24 define aprimary flowpath 26 therebetween. A fluid, for example, steam isdirected from steam inlet 23 along the primary flowpath 26, which urgesrotation of the rotor 12 about the axis 14.

FIG. 2 illustrates a radial view of a sector of a first stage 30 withaxial female tree dovetail slots 32 cut in the rotor drum 13. At thebase of the female tree dovetail slot 32 is a channel 34 cut to accept atwist lock device (not shown) that is used to axially lock in place themale tree dovetail 50 of the buckets 16.

The buckets may be assembled onto the wheel (rotor) in the axialdirection. A stopping/locking mechanism is provided that will hold thebucket in place. FIG. 3 illustrates a side view of a twist lock device40 adapted for holding axial entry dovetailed buckets in axialdovetailed slots. The twist lock device 40 includes a center pin 42 withheads 44 at each end of the center pin. The head 44 at a first end ofthe center pin 42 is formed as a half head 46 and includes a stakingtab. The head 44 at the second end of the center pin 42 includes a fullhead 48. The channel 34 in the rotor is sized for the center pin. Thelength 43 of the center pin 42 is set to match the channel with the halfhead 46 outside the front face of the rotor and second head 48 of thepin outside the downstream face of the rotor stage.

Before the buckets are installed, the twist lock device 40 is positionedsuch that the half head 46 is oriented in the inward radial direction.The twist lock device 40 is then lowered into the channel 34 below thefemale dovetail slot 32 into the rotor drum. FIG. 4 illustrates thetwist lock device 40 in place within the channel 34 of female dovetailslot 32 in preparation for axial insertion of a bucket male treedovetail. If the twist lock device 40 is inserted into wheel (rotor)dovetail with the half head 46 in an outward radial orientation, thehalf head 46 will block sliding the axial entry male dovetail 50 of thebucket inside the wheel (rotor) slot.

The axial entry male dovetail 50 of the bucket is then slid into thewheel (rotor) slot in the axial direction. With the axial entry maledovetail bucket in place, the twist lock device 40 is rotated by 180degrees such the half head 46 oriented outward radially and flat surface45 is radially inward as shown in FIG. 5 The head 46 for the twist lock20 will be bent inside a wheel staking groove 47 in the wheel (rotor)face 49 as shown in FIG. 6. Insufficient space is available on thedownstream side for staking so the twist lock device 40 has a fullcylindrical head 48 on the downstream side. Staking of the twist lockdevice 40 prevents axial movement of the installed bucket. Other bucketsmay be installed in a similar manner.

In a further aspect of the invention, when the female tree dovetails arecut in the drum for the stage, an annular space downstream of the stagesection is also cut into the rotor drum to allow a space for the cuttingtool to be removed. A spacer ring forming at least a sector of theremoved downstream annular space is installed to facilitate installationof the buckets. The thickness of the spacer ring is set to limit theinsertion of the male dovetail for the bucket, thereby establishingproper axial orientation. After the buckets have been inserted theproper axial distance and locked in place, the spacer is removed.

FIG. 7 illustrates an expanded radial view of a cooling space 70 betweenthe male dovetail 50 of the first stage bucket and a complimentary maleprojection of the rotor drum 13. The male dovetails include an expandedspace 75 at an outer end that provides the axial channel for the flow ofcooling steam. The channel discharges into a low-pressure channeldownstream that will be described in greater detail below.

FIG. 8 illustrates a cutaway axial view of a cooling path 70 for a rotordrum 13 with axial entry dovetailed bucket 116 installed rotor drum 13.The annular space 60 downstream from the bucket includes the spacer 65(shown prior to removal). The staked twist lock device 40 axially holdsthe male dovetail 50 (FIG. 6) of the bucket 116 in place within therotor drum 13. FIG. 8 also illustrates the axial flow channel 70 forcooling steam 72. The cooling steam 72 is received from the annularspace 60 downstream of the reaction stage where, for a reaction stage,the pressure is higher than the upstream side but the steam temperatureis substantially cooler. The cooling steam 72 may pass through the axialspace 70 between the male dovetail of the bucket and the female dovetailcut into the drum rotor.

FIG. 9 illustrates a reaction first reaction stage 110 with an axialentry dovetailed bucket 116. The bucket 116 with male dovetail 50 isdisposed between an upstream first stage nozzle 114 and a downstreamsecond stage nozzle 118. The dovetailed bucket 116 is installed axiallyin the dovetailed slots in the rotor drum 13. The nozzle 114, 118 may besupported by an outer casing (not shown). The nozzles 114, 118 mayinclude various seals mounted on end shrouds 27 to prevent leakage pastthe nozzle blades 115, 119. The seals may include tooth seals, J-seals,and labyrinth seals. The axial channel 70 through the space between themale dovetail of the bucket and the slot of the drum rotor may directthe downstream cooling steam to the low-pressure channel leakoffdischarge path 140. The labyrinth seal 132 on the first stage nozzle 114prevents higher pressure from the nozzle block 23 in the downstreamleakoff path. The higher pressure from the nozzle block 23 could preventthe cooling flow through the cooling path. Similarly, the tooth seal orthe J-seal may limit leakage between the first stage nozzle 114 and thefirst stage bucket 116 from entering the leakoff path 140 and therebylimiting cooling flow 72.

In a further aspect of the present invention, first stage tangentialentry buckets 150 with blade 151 in rotor drum 13 of rotor 12 isdisposed between first stage nozzle 114 with blade 115 and second stagenozzle 118 with blade 119. The bucket 150 dovetail 153 may be providedwith a cooling passage that utilizes higher pressure steam P2 165downstream from the bucket 150 of a reaction stage 110 to cool the rotordrum 13 as illustrated in FIG. 10. An axial cooling passage 155 isprovided between the bucket 150 and the next nozzle 118. The coolingpassage 155 through root 180 of bucket 150 again discharges coolingsteam to the low-pressure leakoff discharge path 140. Seals 131 and 132limit leakage from steam inlet 23 and from space between first stagenozzle 114 and first stage bucket 150 from entering the leakoff path 140and thereby limiting cooling flow.

While the invention has been described in detail in connection with onlya limited number of embodiments, it should be readily understood thatthe invention is not limited to such disclosed embodiments. Rather, theinvention can be modified to incorporate any number of variations,alterations, substitutions or equivalent arrangements not heretoforedescribed, but which are commensurate with the spirit and scope of theinvention. Additionally, while various embodiments of the invention havebeen described, it is to be understood that aspects of the invention mayinclude only some of the described embodiments. Accordingly, theinvention is not to be seen as limited by the foregoing description, butis only limited by the scope of the appended claims.

1. A rotor of a turbomachine comprising: a rotor drum disposed at acentral axis; a plurality of dovetailed buckets for a stage of theturbomachine, wherein the plurality of dovetailed buckets are secured tothe rotor drum at mating surfaces within a corresponding plurality ofdovetailed slots cut in the rotor drum; at least one cooling passageformed within the rotor drum for the stage of the turbomachine; and alow pressure sink disposed at an upstream end of the rotor drumreceptive of a coolant flow through the cooling passage.
 2. The rotor ofclaim 1, wherein the stage if a first stage, reaction stage for a rotorof a steam turbine.
 3. The rotor of claim 2, wherein the coolant flowcomprises steam routed into the cooling passage from a downstreamportion of the steam turbine including a space immediately downstreamfrom each of the plurality of dovetailed bucket in the stage.
 4. Therotor of claim 3, wherein the plurality of dovetailed slots are cut inthe rotor drum for axial entry of the plurality of dovetailed buckets.5. The rotor of claim 4, wherein the at least one cooling passage formedwithin the rotor drum for the stage of the turbomachine comprises atleast one space formed between a male dovetail of the dovetailed bucketand a complimentary male projection of the rotor drum.
 6. The rotor ofclaim 3, wherein the plurality of dovetailed slots are cut in the rotordrum for tangential entry of the plurality of dovetailed buckets and theat least one cooling passage formed within the rotor drum for the stageof the turbomachine comprises a hole bored axially through a root of thebucket above the dovetail.
 7. The rotor of claim 1, further comprising:an axial through-hole of the rotor drum at a base of each dovetail slotof the plurality of dovetail slots; and a twist-lock device installed inthe axial through-hole of the rotor drum and adapted for the axiallyretaining the dovetailed bucket, the twist lock device including acenter pin, a retaining head at each end of the center pin wherein aforward head includes a rotatable half-head, being rotatable to aninward radial position allowing entry of the dovetailed bucket into thedovetailed slot and being rotatable to an outward radial positionretaining the dovetailed bucket in the dovetailed slot.
 8. The rotor ofclaim 7, further comprising: an annular spacer adapted to mount aroundthe rotor drum between a first stage and a second stage for temporaryuse during insertion of dovetailed buckets into axial dovetail slots ofthe rotor drum, wherein an axial length of the annular spacer is sizedfor axial positioning of the plurality of dovetailed buckets.
 9. Therotor of claim 1, comprising: at least one rotor drum through holeextending from the cooling passage to the low pressure sink, wherein thelow pressure sink comprises at least a root spill of the a first stage.10. The rotor of claim 9, further comprising: sealing means between anupstream root of the plurality of buckets and the root spill of thefirst stage, wherein the sealing means include J-seals.
 11. Amulti-stage steam turbine comprising: a stator disposed at a centralaxis; and a rotor disposed radially inboard of the stator including: arotor drum; a plurality of dovetailed buckets for a stage of the steamturbine, wherein the plurality of dovetailed buckets are secured to therotor drum at mating surfaces within a corresponding plurality ofdovetailed slots cut in the rotor; at least one cooling passage formedwithin the rotor drum for the stage of the turbomachine; and a lowpressure sink disposed at an upstream end of the rotor receptive of acoolant flow through the cooling passage.
 12. The rotor of claim 11wherein the stage of the steam turbine is a first stage reaction stage.13. The steam turbine of claim 12 wherein the coolant flow comprisessteam routed into the cooling passage from a downstream portion of thesteam turbine including a space immediately downstream from each of theplurality of dovetailed bucket in the stage.
 14. The rotor of claim 13wherein the plurality of dovetailed slots are cut in the rotor drum foraxial entry of the plurality of dovetailed buckets.
 15. The rotor ofclaim 14 wherein the at least one cooling passage formed within therotor drum for the stage of the turbomachine comprises at least onespace formed between a dovetail of the dovetailed bucket and acomplimentary male projection of the rotor drum.
 16. The rotor of claim12 wherein the plurality of dovetailed slots are cut in the rotor drumfor tangential entry of the plurality of dovetailed buckets.
 17. Therotor of claim 16 wherein the at least one cooling passage formed withinthe rotor drum for the stage of the turbomachine comprises a hole boredaxially through a root of the bucket above the dovetail.
 18. The rotorof claim 1 comprising at least one rotor drum through hole extendingfrom the cooling passage to the low pressure sink.
 19. The rotor ofclaim 1, further comprising: an axial through-hole of the rotor drum ata base of each dovetail slot of the plurality of dovetail slots; and atwist-lock device installed in the axial through-hole of the rotor drumand adapted for the axially retaining the dovetailed bucket, the twistlock device including a center pin, a retaining head at each end of thecenter pin wherein a forward head includes a rotatable half-head, beingrotatable to an inward radial position allowing entry of the dovetailedbucket into the dovetailed slot and being rotatable to an outward radialposition retaining the dovetailed bucket in the dovetailed slot.
 20. Amethod for installing axial entry dovetailed buckets into dovetail slotsof a stage of a drum rotor, the method comprising: inserting a twistlock device into an axial through-hole in a base of a dovetail slot of astage of a drum rotor for each of a plurality of dovetailed buckets;orienting a half-head of a front head of the twist lock device in aninward radial direction; inserting a spacer in a space in the drum rotorbetween a stage and a succeeding stage; fully inserting the dovetailedbucket into the dovetail slot of the stage of the rotor drum; orientingthe half-head of the front head of the twist-lock device in an outwardradial direction; and removing the spacer.